Choreo

I currently have the 17" x 18" stock configuration of thinspokes on my car.

If I switch to a new set of thinspokes - all 18" x 9.5"...

(1) Will the front wheels rub or hit on anything with the larger diameter?

(2) Do I need to reprogram anything for the Speedometer/Odometer, etc?

65GGvert

You'll have to have rear tires on those wheels that maintain a difference of .5 to 1.5" larger diameter or you'll get traction and active handling errors when you drive.

alxltd1

I ran 18x9.5 OEM polished Thin Spokes on all four corners. 275x35x18 up front 295x35x18 on the rear. No rubbing or any other issues. They were the stock rear wheels and had 65mm offsets as well. As long as you keep the overall diameter of wheel and tire close to stock you should not have a TC or speedo issue.

Vetteman Jack

Choreo

OK. This brings up another related question. As far as I can tell Michelin only sells one 18" size in their AS/ZP Runflat (275/40R18 99Y RF INI). So I am assuming that if I am sold on running Michelin RunFlats, running 18" all around may not be a good idea?

alxltd1

If you are talking about the Pilot Sport AS/ZP they make it in a 245x40R18 as well, which would give you the proper rake front to rear ( using the 245 in front the 275 on the rear would give you a 1 inch rake) but the 245 tire would be too stretched over the 9.5 rim. So yes, if you are sold on only this tire, 18x9.5 all around is not a good idea.

Choreo

Thanks! That solves that brainstorm!

spdislife

Not necessarily. I know a lot of guys who run a square setup and have no A/H issues.

65GGvert

No you don't. You may know guys who run a square WHEEL size set up, but if the overall tire diameter is the same on all four, they do have A/H issues.

Black0ut

I've run 295/30/18 square, 305/35/18 square and had ZERO A/H and T/C issues. Exact same diameter front and rear wheels/tires- I mean, that's the whole point to running a square set up, so you can rotate wheels and get more life out of your tires while increasing the handling characteristics of the car.

Hell, I've even ran taller fronts than rears (275/40/17 front and 305/30/18 rears) and had ZERO a/h and t/c issues.

jcsperson

There are a number of guys running a fully-square setup on the street, wheels and tires, and reporting no issues whatsoever. This same discussion comes up a couple times every year. Here is a fairly recent one:

Pros/Cons of going to 4 18x10.5 instead of stock

65GGvert

Maybe your cars don't have active handling.

alxltd1

Regardless of the debate above, for which I have not opinion or real life experience with, the OP's issue is that he wants to run a particular brand and type of tire on a 18x9.5 rim. The tire he wants only comes in 245x40 and 275x40 in 18. It will give him a 1 inch rake but the 245x40 on a 18x9.5 will be much to stretched I think. So unless he changes tires or rims, or wants to chance running square with the 275x40x18 he is out of luck.

Black0ut

That's suggesting that a majority of people running square setups are driving pre 98 (or whatever year A/H stopping being an option) corvettes. I for one am fairly certain that my 2003 model year car has active handing.

My super old setup had 9mm taller tires in the front than the rear.
My last setup before square had 8mm taller tires in the rear than the front.

If people are running tires that are ~3-~10mm different in diameter... how is running a 0mm difference going to cause issues? There is no way GM's system is that sensitive- the change in diameter is almost negligible.

According to tirerack 9.5in is the max wheel width for a 245 cross section tire- so he might be okay.

OP could also move up one size in each (245 to 255 or 265, and 275 to 285) and see if anything works.

For simplicity sake and ease of use for shopping for a spare (if need be) I would just get 275 or 285 square and be done with it. From my own personal experience, I've had no issues. But maybe my A/H system is just lazy or one off- who knows.

alxltd1

[QUOTE=Black0ut;1586467405]That's suggesting that a majority of people running square setups are driving pre 98 (or whatever year A/H stopping being an option) corvettes. I for one am fairly certain that my 2003 model year car has active handing.

My super old setup had 9mm taller tires in the front than the rear.
My last setup before square had 8mm taller tires in the rear than the front.

If people are running tires that are ~3-~10mm different in diameter... how is running a 0mm difference going to cause issues? There is no way GM's system is that sensitive- the change in diameter is almost negligible.



According to tirerack 9.5in is the max wheel width for a 245 cross section tire- so he might be okay.

OP could also move up one size in each (245 to 255 or 265, and 275 to 285) and see if anything works.For simplicity sake and ease of use for shopping for a spare (if need be) I would just get 275 or 285 square and be done with it. From my own personal experience, I've had no issues. But maybe my A/H system is just lazy or one off- who knows.[/QUOTE]

9.5 is at the very outer limit for a 245, I would not chance it, but thats me.

Problem is the tire he wants ONLY comes in 245x40 and 275x40 in 18. So again he either has to change his choice of tires to get other size availability or run the 275 square and chance any issues with TC A/H.

Choreo

Thanks for all the responses so far.

I currently have Michelin AS/ZP PLUS run flats on my stock 17/18 setup:

Fronts: 245/45/ZR-17
Rears: 275/40/ZR-18

I have another new matching set of Chrome 17/18 GM Speedline Thinspoke wheels on order. Was just thinking I might try using the the 18's all around since my old wheels still look like new.

65GGvert

Put em on there and then post back what happens when you drive.
That should make one of us wrong. Don't forget to follow up and post though, be sure to include the tire sizes when you do.

65GGvert

Here's some guys who do it and they have to turn off a/h, t/c.

http://forums.corvetteforum.com/c5-g...-and-rear.html

65GGvert

Look what's in c5 tech today:

http://forums.corvetteforum.com/c5-t...and-tires.html

Choreo

Yeah... think I will just stay with the stock 17/18 and avoid the headaches.